As a valve train device for an engine, there is known a configuration, in which a plurality of cam portions whose shapes are different from each other are provided for each valve, and valve opening amounts or valve opening timings of intake valves and exhaust valves are switchable depending on an operating condition of an engine by selecting a cam portion for use in opening and closing a valve from among the cam portions.
For instance, Patent Literature 1 describes a valve train device provided with a camshaft including a shaft portion, and a tubular cam element portion which is mounted on the shaft portion to be displaceable relative to the shaft portion in the axial direction of the shaft portion, and to be integrally rotatable with the shaft portion; and an actuator which causes the cam element portion to move in the axial direction, wherein the positions of a plurality of cam portions provided in the cam element portion are changed by moving the cam element portion in the axial direction for switching the cam portions for use in opening and closing valves.
The valve train device is provided with the actuator including pin members at both sides of the cam element portion, wherein the pin members are operative to advance or retract (project/retract) in a direction orthogonal to the axial direction. The valve train device is configured to move the cam element portion in the axial direction, namely, to switch a cam portion by selectively operating (projecting) the pin members depending on the position of the cam element portion, and by causing the pin members to come into contact with end surface cams provided at both ends of the cam element portion in the axial direction.
In a valve train device, it is required to repeatedly switch a cam portion in a short period of time depending on an operating condition of an engine. When a response delay or an operation failure occurs in an actuator, however, pin members of the actuator located at both sides of a cam element portion may be simultaneously set to an operative state. In this case, the cam element portion may be made non-rotatable due to axial restriction the cam element portion by the pin members from both sides in association with rotation of the cam element portion. Therefore, it is required to avoid the aforementioned drawback in advance.